1. Field of the Invention
This invention relates to coloring fine particles and toners for developing electrostatic images using said particles. More specifically, it relates to coloring fine particles wherein a coloring agent is uniformly dispersed throughout and the particle surface is modified, so rendering the particles suitable for use as toners, paints, inks, resinous coloring materials and the like, and whereby the use of said coloring fine particles as toners in laser printers, liquid crystal printers and other printing devices to develop an electrostatic image permits a clear image to be obtained.
2. Description of the Prior Art
In electronic photography, a latent electrical image is formed on a photosensitive support comprising a photoconducting material such as selenium, lead oxide or cadmium sulfide, developed by a powder developer, transferred to paper or another support, and then fixed.
In the prior art, the toners used for developing electrostatic images were generally manufactured by adding coloring agents and other additives (charge control agents, offset inhibitors and lubricants, etc.) to a thermoplastic resin, melting the mixture to disperse these agents in the resin, microgrinding the solid obtained, and classifying the resulting particles so as to obtain coloring fine particles with the desired particle diameter.
There were, however, several disadvantages associated with the manufacture of toner by this grinding method. Firstly, the method necessarily involved a large number of processes including manufacture of the resin, kneading the resin together with coloring agents and other additives, grinding the solid obtained, and classifying the ground particles to obtain coloring fine particles with the desired particle diameter. A considerable amount of equipment was consequently involved, and the toner manufactured by this method was necessarily expensive. In particular, the classification process was an essential step to obtain toner with the optimum range of particle diameters to produce a clear image with very little fogging, but there were problems as regards productivity and yield. Secondly, in the kneading process, it was extremely difficult to distribute the coloring agent and other additives uniformly in the resin. As a result, the coloring agent and charge control agents were poorly distributed in the toner, the frictional charge of individual particles was different, and the degree of resolution of the resulting image was poor. Moreover, there is a tendency to wake toner particles smaller as this is a necessary condition to achieve higher quality images, so such problems are liable to worsen in future. There is a limit to the ability of present grinding machines to produce toners with small particles, but even if small particles can be obtained, the coloring agents and charge control agents are poorly distributed so there is considerable scattering of the electrostatic charge.
In order to resolve these various problems associated with toners produced by grinding methods, other methods of manufacturing toners have been proposed such as emulsification polymerization and suspension polymerization (Patent Publications Nos. SHO 36(1961)-10231, SHO 43(1968)-10799, SHO 47(1972)-518305, and SHO 51(1976)-14895). In one such method, coloring materials such as carbon black and other additives are added to a polymerizable monomer, and emulsification or suspension polymerization is carried out so as to synthesize a toner containing coloring material in one step. This provides a considerable improvement on conventional grinding methods, and as no grinding process is involved whatsoever, there is no need to improve the brittleness of the product. Moreover, as the particles formed are spheroidal, they have excellent fluidity and their frictional charge is uniform.
There are, however, some problems even with the manufacture of toners by polymerization. Firstly, as the hydrophilic substances such as dispersing agents and surfactants used in the polymerization, cannot be completely removed even by washing and remain on the surface of the toner, the electrostatic properties of the toner are easily affected by the environment. Secondly, as the toner particles obtained by polymerization are spheroidal and have a very smooth surface, toner which adheres to the photosensitive support is difficult to remove and cleaning is ineffective.
Various methods have been proposed to resolve these problems, for example as disclosed in Japanese Patent Laid-Open Nos. SHO 61(1986)-255354, SHO 53(1978)-17736, SHO 63(1988)-17460, and SHO 61(1986)-167956, but either they were not completely effective or they led to increased cost.
An object of the present invention is, therefore, to provide a new type of coloring fine particles, a method for manufacturing them, and a toner for developing electrostatic images using these particles.
Another object of the present invention is to provide coloring particles wherein a coloring agent is uniformly distributed throughout and the particle surface is modified, a method for manufacturing the particles, and a toner using the particles for developing a clear, electrostatic image.